The prior art includes, as disclosed in EP-A-481,732, a sustained-release preparation comprising a drug, a polylactic acid and a glycolic acid-hydroxycarboxylic acid [HOCH(C.sub.2-8 alkyl)COOH] copolymer. The disclosed process comprises preparing a W/O emulsion consisting of an internal water phase comprising an aqueous solution of a physiologically active peptide and an external oil phase comprising a solution of a biodegradable polymer in an organic solvent, adding said W/O emulsion to water or an aqueous medium and processing the resulting W/O/W emulsion into sustained-release microcapsules (drying-in-water method).
EP-A-52510 describes a microcapsule comprising a hormonally active polypeptide, a biodegradable polymer and a polymer hydrolysis control agent. The disclosed process for its production is a coacervation process which comprises adding a coacervation agent to a W/O emulsion consisting of an aqueous solution of the polypeptide as the internal water phase and a halogenated organic solvent as the oil phase to provide microcapsules.
GB-A-2209937 describes a pharmaceutical composition comprising a polylactide, a polyglycolide, a lactic acid-glycolic acid copolymer or a mixture of these polymers and a water-insoluble peptide. Also disclosed is a production process which comprises dispersing a salt of the water-insoluble peptide in a solution of said polylactide, polyglycolide, a lactic acid-glycolic acid copolymer or a mixture of these polymers, removing the solvent by evaporation and molding the resulting mixture into solid particles.
EP-A-58481 describes a process for producing a pharmaceutical composition comprising a polylactide and an acid-stable polypeptide which, for instance, comprises dissolving tetragastrin hydrochloride and a polylactide in aqueous dioxane, casting the solution into a film and evaporating the solvent.
EP-A-0467389 teaches a technology for providing a drug delivery system for proteins and polypeptides by the polymer precipitation technique or the microsphere technique. However, this literature contains no specific disclosure about a system containing an LH-RH derivative.
The luteinizing hormone-releasing hormone, known as LH-RH (or GnRH), is secreted from the hypothalamus and binds to receptors on the pituitary gland. The LH (luteinizing hormone) and FSH (follicle stimulating hormone), which are released thereon, act on the gonad to synthesize steroid hormones. As derivatives of LH-RH, the existence of both agonistic and antagonistic peptides is known. When a highly agonistic peptide is repeatedly administered, the available receptors are reduced in number so that the formation of gonad-derived steroidal hormones is suppressed. Therefore, LH-RH derivatives are expected to be of value as therapeutic agents for hormone-dependent diseases such as prostate cancer, benign prostatomegaly, endometriosis, hysteromyoma, metrofibroma, precocious puberty, mammary cancer, etc. or as contraceptives. Particularly, the problem of histamine-releasing activity was pointed out for LH-RH antagonists of the so-called first and second generations (The Pharmaceuticals Monthly 32, 1599-1605, 1990) but a number of compounds have since been synthesized and recently LH-RH-antagonizing peptides having no appreciable histamine-releasing activity have been developed (cf. U.S. Pat. No. 5,110,904, for instance). In order for any such LH-RH antagonizing peptide to manifest its pharmacological effect, there is a need for a controlled release system so that the competitive inhibition of endogenous LH-RH may be persistent. Moreover, because of histamine-releasing activity which may be low but is not non-existent in such peptides, a demand exists for a sustained-release preparation with an inhibited initial burst immediately following administration.
Particularly, in the case of a sustained-release (e.g. 1-3 months) preparation, it is important to ensure a more positive and constant release of the peptide in order that the desired efficacy may be attained with greater certainty and safety.
At the same time, there is a long-felt need for a method of producing a sustained-release preparation having a high peptide trap rate for a physiologically active peptide, particularly LH-RH-antagonizing peptides.